Valves are used to control gases or other fluids in various types of apparatus and vehicles, such as aircraft. For example, valves may be used to control the supply of air between a compressor and a turbine of a gas turbine engine, and to thereby control the supply of air to bearings for thrust balancing of the gas turbine engine, for example, in aircraft. In certain applications, for example during takeoff of aircraft, it may be desirable to control the supply of air, for example to the bearings, such that air flows only when there is a relatively high inlet pressure, and such that air flows at a relatively large volume once a sufficient inlet pressure is attained. It may also be desirable to be able to vary the inlet pressure at which the air is supplied. In addition, for valves having a spring, it may be desirable to reduce the size and/or weight of the spring needed to operate the valve.
Accordingly, it is desirable to provide a valve for air control, such as in a gas turbine engine of an airplane, that opens only when there is a relatively high inlet pressure and/or at a relatively large volume once the relatively high inlet pressure is attained, and/or that can be adjusted to vary the inlet pressure at which the air is supplied, and/or for which a relatively smaller spring can be utilized. It is further desirable to provide a gas turbine engine, such as in an airplane, having a valve for air control, that opens only when there is a relatively high inlet pressure and/or at a relatively large volume once the relatively high inlet pressure is attained, and/or that can be adjusted to vary the inlet pressure at which the air is supplied, and/or for which a relatively small spring can be utilized.